Chloride-containing Electrolyte Research Articles

ATR-SEIRAS––an approach to probe the reactivity of Pd-modified quasi-single crystal gold film electrodes

Quasi-single crystalline gold films of 20 nm thickness and preferential (1 1 1) orientation on Si hemispheres were modified by controlled potentiostatic deposition of Pd (sub-ML, ML, multi-L) from sulphate and/or chloride-containing electrolyte. The electrochemical properties of these model electrodes were characterised for hydrogen and (hydrogen-) sulphate adsorption as well as for surface oxide formation by cyclic voltammetry. Conditions were developed to fabricate defined and stable Pd monolayers. In situ ATR-SEIRAS (Attenuated Total Reflection Surface Enhanced Infrared Reflection Absorption Spectroscopy) experiments were carried out to describe the electrochemical double layer of Pd modified gold film electrodes in contact with aqueous 0.1 M H 2SO 4 with focus on interfacial water and anion adsorption. Based on an analysis of the non-resonant IR background signal the potential of zero charge is estimated to 0.10–0.20 V (vs. RHE). CO was found to be weakly physisorbed in atop sites on Au(1 1 1-20 nm)/0.1 M H 2SO 4 only in CO saturated electrolyte. CO, deposited on a quasi-single crystal gold film modified with 1 ML Pd, is chemisorbed with preferential occupation of bridge sites and atop positions at step edges. Saturated CO adlayers, as obtained by deposition at 0.10 V, contain isolated water species and are covered by a second layer of hydrogen bonded water. Potentiodynamic SEIRAS experiments of CO electro-oxidation on Pd-modified gold film electrodes demonstrate clearly the existence of a “pre-oxidation” region. They also provide spectroscopic evidence that isolated water and weakly hydrogen bonded water are consumed during the reaction and that atop CO on defect sites is a preferential reactant. The simultaneous in situ monitoring of the potential- and time-dependent evolution of characteristic vibrational modes in the OH- and CO-stretching regions are in agreement with the Gilman (“reactant pair”) mechanism of CO oxidation.

On the Effect of OH–Ions on the Inhibition of Steel Corrosion with Amines

The combined effect of amines and OH– ions on the corrosion resistance of steel in chloride-containing aqueous electrolytes was studied. The role of the chemical structure of amines in the inhibition of steel depassivation was analyzed, with the alkalifying and adsorption effects being separated out. Synergism of some amines and OH– ions makes it possible to create effective inhibitive formulations.

Pit Initiation at Single Sulfide Inclusions in Stainless Steel: II. Detection of Local pH, Sulfide, and Thiosulfate

Small wires of W, Ag, and Pt were placed within an electrochemical microcell above single sulfide inclusions to detect the pH, sulfide, and thiosulfate, respectively. In chloride-free electrolytes the onset of sulfide dissolution was accompanied by a decrease in pH of 0.5 units to 4.2, a value that is not low enough to initiate active metal dissolution. In chloride-containing electrolytes, metastable pitting events were found to cause rapid temporary periods during which the pH decreased to values as low as zero. However, the results suggest that sustained pH decreases occur only with onset of stable pitting. Sulfide species were only detected during chemical dissolution in a pH 2 electrolyte at the rest potential and not as a result of anodic dissolution at neutral pH. A Pt wire along with an iodide/triiodide couple was used to detect thiosulfate as a result of anodic dissolution. The results support the mechanism of electrochemical dissolution of sulfide inclusions to produce thiosulfate at neutral pH. © 2002 The Electrochemical Society. All rights reserved.

Optically scanning the morphology of protective layers and forecasting the corrosion resistance of thermally oxidized steel

The results of investigating the morphology and protective properties of surface layers obtained on chromium steel Х18Н10Т by oxidizing in air at a temperature of 140 to 950°C are considered. After a special digital treatment, the scanned optical images of a small surface area probed allow one to introduce and determine those parameters of the morphological nonuniformity of the thermal oxide layer which affect its protective ability. Corrosion tests of oxidized specimens confirmed the applicability of the scanner morphological control to predicting the protective properties of thermal coatings against pit corrosion in chloride-containing electrolyte solutions.

The electrochemical behaviour of CuZn under conditions of illumination

The influence of UV illumination on the passive behaviour of Cu37Zn in pH 9.2 and 13.0 chloride-containing electrolytes was studied using potentiodynamic polarisation tests, cyclic voltammetry and complex impedance spectroscopy. It was found that UV illumination exerted a slight activating effect on the passive behaviour in the alkaline pH 13.0 solution, with slightly higher passive current densities being recorded under conditions of illumination. A more pronounced UV illumination effect was observed in the pH 9.2 solution. This was characterised by a 4-fold increase in the passive current density, a shift in the breakdown potential by 250 mV in the active direction, a decrease in the charge transfer resistance and an increase in the double layer capacitance. These results are explained in terms of the nature of the passive film on CuZn, which consists of a complex layer involving ZnO · xH 2O and Cu 2O/CuO. On illumination, photo-decomposition of the n-type ZnO phase occurs leading to a modification of the passive layer rendering it more susceptible to pitting attack in the chloride environments.

AC impedance study on corrosion of 55%Al–Zn alloy-coated steel under thin electrolyte layers

The corrosion behavior of 55%Al–Zn alloy-coated steel under a chloride-containing electrolyte layer ranging from 15 to 888 μm in thickness has been investigated using electrochemical impedance spectroscopy (EIS). The interface of the coating-electrolyte layer can be represented by an equivalent circuit consisting of a solution resistance, a charge transfer resistance, a double layer capacitance and a Warburg element. The corrosion current density estimated from the polarization resistance significantly decreases as the thickness of electrolyte layer increases between 15 and 100 μm and is almost independent of the thickness up to 888 μm. Furthermore, corrosion monitoring of 55%Al–Zn alloy-coated steel has been performed under alternate conditions of 1 h-immersion in solution of 0.05 M NaCl or 0.05 M Na 2SO 4 and 7 h-drying at 298 K and 60% RH. During the wet–dry cycles, the instantaneous corrosion rate was monitored by AC impedance method together with the corrosion potential. The corrosion rate increases at the initial stage of the wet–dry cycles because the native oxide on the coating surface is dissolved into the solution and converted to hydrated zinc and aluminum oxides, and then decreases slowly owing to the accumulation of the corrosion products over the coating surface. The corrosion mechanism of 55%Al–Zn coating is discussed on the basis of the monitoring results.

Lead deposition onto fractured vitreous carbon: influence of electrochemical pretreated electrode

We evaluated the electrochemical deposition of Pb(II) onto Fractured Vitreous Carbon (FVC) electrodes from solutions containing very low concentrations of lead in different electrolytes (sulfate or chloride). To examine how the FVC surface state influences the lead deposition efficiency, the electrodes were subjected to different electrochemical pretreatments prior to the actual deposition process. The FVC electrode was used as a representative model of the vitreous carbon (VC) bulk, avoiding the polishing procedure that could change the surface. Electrochemical pretreatment was carried out by cyclic voltammetry in electrolytes containing chloride or nitrate anions and in some cases, ferrocyanide. Before and after the electrochemical pretreatment, the electrode surface morphology was assessed using Atomic Force Microscopy (AFM) imaging. The quantity of lead deposited on the FVC electrode surface (lead deposition efficiency) in each experiment was estimated from the charge under the lead anodic, dissolution peak. Electrochemical pretreatment of electrodes in chloride or nitrate electrolytic baths consistently reduced the lead deposition efficiency. A detailed analysis, correlating lead deposition efficiencies to surface roughness and fractal dimension of the freshly prepared and electrochemically pretreated FVC electrodes, indicated that the decrease in efficiency corresponded to the change in electrode surface geometry. The greater efficiency of lead deposition observed in the chloride-containing electrolyte was due to the interaction between chloride and deposited lead rather than a chloride interaction with the FVC substrate.

Anion influence in lead removal from aqueous solution by deposition onto a vitreous carbon electrode

We investigated the electrolytic removal of Pb(II) from aqueous solutions containing different electrolytes (nitrate, chloride or sulfate), by electrolysis onto reticulated vitreous carbon electrode (RVC). The efficiency of the electrolytic process of lead removal was found to be a function of electrolyte composition. The chloride containing electrolyte, provided the highest efficiency of lead removal, while removing Pb(II) from the sulfate electrolytes turned out to be a very difficult and high energy consuming process. Cyclic voltammetry and the atomic force microscopy (AFM) were used to characterize lead deposits on RVC and fractured vitreous carbon (FVC) electrodes surface. Our study showed that in the chloride solution, a significantly larger amount of lead deposit was formed than in the sulfate electrolyte. Since the same phenomenon was observed with both electrode types, the FVC electrode is established as an appropriate laboratory model for studying the RVC, which is often used in industrial applications. AFM analysis revealed that lead deposits formed from different electrolyte solutions possess different surface morphologies, indicating different mechanism of formation or different kinds of interactions between the metal adlayer and the adsorbed anions. A highly dense lead deposit, spread all over the electrode surface, in the form of a 2-D film, was found when using the chloride-containing electrolyte. This was attributed to the surface annealing effect and the increased number of nucleation sites due to chloride coadsorption at the electrode surface. Deposits formed from the sulfate electrolyte consisted of numerous, isolated and rather small lead clusters, indicating that deposition from sulfate solutions was inhibited by the formation of the passivated salt adlayer over the lead clusters.

Cu deposition onto n-GaAs(100): optical and current transient studies

Abstract The deposition of Cu from sulphuric and hydrochloric acid solutions onto n-GaAs(100) has been studied by a combination of electrochemical and optical techniques. Reflectance-potential curves allowed Cu deposition and dissolution to be monitored in the presence of side reactions which, particularly in chloride-containing electrolytes, mask the deposition process in the cyclic voltammograms. Nucleation and growth of the Cu clusters on n-GaAs(100) has also been investigated by potential step experiments and the resulting current transients analyzed in terms of standard nucleation models. Cu was found to deposit via progressive nucleation, even onto GaAs surfaces which were covered by a ruthenium adlayer. The nucleation rate for the Ru-modified surface was clearly lower than for bare n-GaAs(100).

Identification of phases in Ag + Pd alloys electrodeposited by the electrochemical ALSV technique

The well-established anodic linear sweep voltammetry (ALSV) technique has been used to identify the phases present in electrodeposited thin layers of Ag+Pd alloys. Alloys were deposited both potentiostatically and galvanostatically on glassy carbon and gold rotating-disc electrodes from a chloride-containing electrolyte at elevated temperatures. It is shown that electrodeposited Ag+Pd alloys appear in two different phases (ordered structures) depending on the chemical composition and the amount (thickness) of electrodeposited alloy. It is also found that the temperature of the electrolyte for alloy deposition and/or dissolution has a slight effect on the ALSV peak potentials but has no influence on the phase composition of the alloy. The concentration of chloride ions in the electrolyte for alloy dissolution (characterization) was found to be a limiting factor in successful and complete dissolution of Ag+Pd alloys.

The activation of aluminium by indium ions in chloride, bromide and iodide solutions

The corrosion and passive behaviour of aluminium in chloride, bromide and iodide solutions in the absence and presence of indium, as activator ions, was investigated using electrochemical techniques. Pit formation mechanisms for aluminium in chloride-, bromide- and iodide-containing solutions appeared to be similar with the caveat that, in the case of iodide anions, liberated iodine attacked the base metal leading to destabilization of the forming film. In addition, the formation of iodic and hypoiodous acids gave rise to the build-up of a highly aggressive pit solution which inhibited repassivation. The difference in the activity of the halide anions was evident also on activation of the aluminium surface by indium ions introduced into the working solution. Greater adsorption of bromide and iodide anions at flawed areas reduced the rate and efficiency of activator deposition at the aluminium surface, with the result that the rate at which the surface was activated was reduced. Activation appeared, also, to be more permanent in chloride-containing electrolytes.

Crevice Corrosion Products of Dental Amalgam

The objective of this study was to determine the in vitro corrosion products that resulted from crevice corrosion of low- and high-copper dental amalgams. Specimens were potentiostatically polarized in a chloride-containing electrolyte while set against a PTFE surface to form a crevice. After 16 h, corrosion products were examined by light microscopy, SEM, EDS, and XRD. Analysis showed the presence of three previously reported products [Sn4(OH)6Cl2, SnO, and Cu2O] and a new product, CuCl, which formed on high-copper, gamma 2-free amalgams. Thermodynamic considerations show that CuCl is stable for the reported in vivo potentials of amalgam restorations and the high acidity and high chloride ion concentration associated with crevice corrosion.

The passivation of nickel in aqueous solutions-IV. Optical and electrochemical investigations of the anodic behavior of nickel in chloride-containing solutions

The passivation behavior of nickel in 0.15 N Na 2SO 4 chloride-free solution is compared with that which occurs in a chloride-containing electrolyte. In situ techniques, such as differential reflectometry and electrochemical polarization, are utilized in this study. The presence of Cl- ions did not alter the composition of the passivating film nor does Cl- alter the mechanisms by which passive film formation occurs. However, Cl − ions delay the growth of a passivating film at pH values of 4 and 8. In these solutions, film breakdown as well as severe pitting occurs subsequent to passivation. In contrast, in solutions of pH 12, the chlorides affect neither the film formation process nor film stability.

Surface structural changes of evaporated thin silver film electrodes during the adsorption of chloride ion

It is well known that the surface of metal electrodes undergoes structural changes when subjected to different electrochemical treatments (potential cycling, upd reactions, etc) [l-5]. The structural changes of silver in certain electrolytes. particularly chloride. have received much attention because of their connection with the appearance of the SERS effect. The capacitance vs. potential curve of single silver crystals in chloride solutions [6] exhibits a narrow peak in the potential range between -0.5 and 0.0 V (vs. SCE), depending on the crystallographic orientation. Apparently this peak does not appear in polycrystalline silver and evaporated silver thin films [7-91. The peak has been attributed to partial charge transfer and later to a rearrangement of the adsorbed surface layer by Valette et al. [6,10] and to a reconstruction of the silver surface layer by Fleishmann et al. [ll]. Voltammetric studies with polycrystalline [12-141 and single crystal (111) [15] electrodes in chloride-containing electrolytes show, in the potential range mentioned above, the appearance of a small, reversible peak before the massive formation of AgCl, involving a charge smaller than a monolayer of AgCl. This peak has been attributed [13] to the formation of a submonolayer of adsorbed AgCl. It has also been found that the charge and the peak potential depend strongly on the pretreatment of the electrode. Hubbard and co-workers [15] have shown by LEED and Auger spectroscopies that on silver (111) this peak corresponds to a transition from a diffuse (1 X 1) to an ordered Ag (111) structure, (6 X fi)R30”. Valette and Parsons [lo], from the charge dependence of the amount of specifically adsorbed chloride on (110) single silver crystals, have proposed a structure of c(5 X 2) for the adsorbed chloride at the potential of the narrow peak in the C vs. E curve. In this paper we will show that the appearance of this peak is connected with profound changes of the capacitative response of evaporated thin silver film electrodes.

Applying AC impedance electrochemical methods to corrosion testing cobalt alloy media

A rapid electrochemical corrosion test for a rigid thin-film (TF) magnetic recording disk has been developed. An AC impedance technique is utilized to provide an estimate of the instantaneous corrosion current for a 1 cm/sup 2/ area of the disk surface exposed to an aqueous electrolyte. Results for tests of CoCr TF media exposed to sulfate- and chloride-containing electrolytes are discussed. >

Some properties of zinc/bromine battery electrolytes

The diffusion coefficients for bromine in zinc bromide solutions containing n-ethyl n-methylmorpholinium bromide have been determined over a range of temperatures and reagent concentrations relevant to zinc/bromine battery electrolytes. Some data were obtained also for potassium chloride-containing electrolytes. Values for solution resistivity and kinematic viscosity are also reported.

Étude spectroscopique des films minces deposés à l'interface par excitation optique des plasmons de surface

Surface plasmons (SPs) are collective charge density waves which are confined to the interfacial region between an active medium ( e.g. silver) and a dielectric (electrolyte). They can be excited by light under the attenuated total reflection condition. We used the focused attenuated total reflection method in which SP excitation is recognized as a dark line in the p-polarized reflected light cone. The presence of an adsorbent or a film leads to modifications in the dispersion curve from which the optical properties of the film can be derived. In this paper we present both theoretical and experimental investigations of thin dielectric films with an optical absorption band. The results show clearly the correlation between the structures which appear in the dispersion curve and the optical properties of the film. In a previous investigation we have studied the pyridine-Ag system and we found that the activation cycle for silver (usually used in surface-enhanced Raman spectroscopy) in a chloride-containing electrolyte and in the presence of pyridine leads to the formation of a surface complex which exhibits an absorption band in the near-IR, a region in which pyridine itself does not absorb. We present here some preliminary results for rhodamine B adsoption on silver in order to correlate quantitatively the optical properties of this well-known dye and the anomalous structures which induces on the SP dispersion curve for silver.

Corrosion resistance of nickel-chromium dental casting alloys

The corrosion resistance of twelve Ni Cr dental casting alloys has been assessed by registrating their potentiodynamic polarization curves, polarization resistance curves, and potential-time curves, in a de-aerated and aerated artificial saliva. It has been found that not only the presence of chromium is needed to reduce the electrochemical activity of such alloys, but also that of molybdenum and manganese. The tendency to passivation is enhanced by these two elements, along with the resistance to pitting in a chloride-containing electrolyte. Alloys with low Cr content and without Mo did always corrode in the tested conditions.